In a conventional gas turbine engine an oil system incorporates an anti-siphon pipe. This pipe returns part of the engine oil flow back to the tank (see FIG. 2). The function of the anti-siphon spill is to provide an excess of oil flow where the engine oil flows need adjusting. The anti-siphon pipe provides an air break in the system to avoid the oil draining to the lowest point in the system. Further, the anti-siphon pipe provides some cooling for a sight glass, used for monitoring the oil reserve, in the oil tank.
However, this arrangement is not capable of providing adequate cooling oil for the sight glass to satisfy the minimum fire protection time required by the FAA and CAA. This problem is particularly apparent as the cooling oil of the conventional arrangement is driven by means associated to the engine speed, thus where the engine is at low power the sight glass is particularly prone to failure through fire damage.
The object of the present invention is to provide the means to deliver adequate cooling oil to the sight glass, whilst maintaining the requirement for excess of oil flow where the engine oil flows need adjusting and an air break in the system.